The invention relates to medical tubular shaft instruments of the type comprising a tubular shaft, a handle at a proximal end of the shaft and a movable working part at the distal end of the shaft. More specifically, the invention relates to medical tubular shaft instruments of the type comprising a shaft having a curvature between the distal end and the proximal end of the shaft, and the handle and the working part of which are operatively connected via a force transmission element extending through the shaft and being movable in a longitudinal direction of the shaft.
A medical tubular shaft instrument known from DE 203 11 293 U1 comprises a tubular flexible shaft at a proximal portion of which a handle is arranged. A distal portion of the tubular shaft is used to introduce jaws into a cavity of a patient during an operation for grasping and/or cutting tissue. The jaws are actuated by a force transmission element being accommodated within the flexible shaft and being movable along the longitudinal direction of the shaft. The force transmission element consists of a number of single segments being in contact with an inner surface of the shaft and being arranged next to each other along the shaft. The single segments are pairwise connected by ball joints.
The force transmission element of the known instrument is capable to transmit pushing forces. For transmitting pulling forces the known force transmission element has an additional flexible rod or cable extending through the single segments of the force transmission element.
The force transmission element of the known medical tubular shaft instrument has the drawback, that the ball joints connecting the single elements of the force transmission element only have pushing force transmission capabilities. Significant pulling forces can only be transmitted by the additional pull rod or cable which, however, increases the costs of the force transmission element. In addition, the assembling of the known medical instrument is exacerbated caused by the complex arrangement of the single segments and the pull rod or cable extending through the single element.
Furthermore, it is a disadvantage that the known force transmission element has poor torque transmission capabilities which are needed, if the jaws of the medical tubular instrument are rotatable about the longitudinal direction of the shaft.
It is easy to understand, that the single segments are not capable of transmitting significant torques from one segment to the other, since the ball head of one single segment which engages into the corresponding ball socket of a second single segment are in principle arbitrarily rotatable to each other about the longitudinal direction of the shaft. Beside this, the known ball joint connections can easily be affected by lateral forces leading to a deformation of the force transmission element which is known as buckling and/or flexing of these elements. These undesired effects typically occur by transmitting significant pushing forces along the axial direction of the force transmission element.
Another medical tubular shaft instrument is known from document DE 295 12 503 U1.
This known medical instrument has a curved shaft whose distal portion can be introduced into a body cavity of a patient. At the distal end of the curved shaft, jaws are arranged for cutting and/or grasping tissue during an operation. The jaws are actuated by a force transmission element being accommodated within the curved shaft and being movable along the longitudinal direction of the shaft. The force transmission element consists of a resiliently flexible material, wherein the diameter of the force transmission element is periodically decreased along the longitudinal direction of the force transmission element. The regions where the diameter is decreased and the regular regions form solid body joints which allow adaption of the curvature of the force transmission element to the curvature of the shaft.
The force transmission element of this known medical tubular shaft instrument comprises poor torque transmission capabilities since the diameter decreased regions of the force transmission element have no significant torsional rigidity. In addition, the diameter decreased regions of the force transmission element are susceptible to material fatigue leading to fractures and cracks within the force transmission element. Furthermore, the force transmission element cannot be used in the curved instruments with a tight bend due to its limited flexibility.